Conveyor belt systems are known that include a series of rollers in order to maintain a desired amount of tension in a conveyor belt in situations, for example, where the belt shifts from a generally horizontal path to an upwardly inclined path. To allow this change of direction in a conveying system with a continuous belt, a hitch is provided including hitch rollers where a pair of adjacent rollers are disposed on either side of a gap in the belt conveying surface. Another hitch roller is used in a 3-roller hitch arrangement for allowing the belt to change directions while keeping tension on the belt extending about the hitch rollers. The placement of this tensioning hitch roller can vary considerably so that in some hitch setups the tensioning roller can be generally aligned or only slightly offset upstream or downstream below the upstream one of the pair of hitch rollers on either side of the conveyor belt gap. In this hitch set up, the pair of hitch rollers on either side of the gap in the belt conveying surface are generally at the same vertical level so that the conveying surface transitions from an upstream, generally horizontal orientation to a downstream, upwardly inclined orientation on either side of the gap.
In another hitch setup, the pair of hitch rollers on either side of the gap are vertically offset with the downstream hitch roller being lower than the upstream hitch roller. In this setup, the conveying surface also transitions from an upstream, generally horizontal orientation to a downstream, inclined orientation. However, there is a vertical drop-off from the upstream horizontal section to the downstream inclined section of the belt conveying surface. In both hitch setups, smaller debris such as nuts or bolts, or thinner products such as envelopes traveling along the belt, may fall into the gap as it passes over the gap or by cascading down an inclined downstream section of the belt conveying surface adjacent the gap, becoming trapped near the tensioning hitch roller.
Hitch guards have been used to provide a smooth transition across the gap in the belt conveyor surface and to cover the gap to minimize the debris falling between the adjacent upper rollers into the gap. One known hitch guard was formed from a bar of UHMW (ultra high molecular weight) polyethylene material with a square cross section that is cut across the diagonal to form two bars with identical triangular cross sections. The triangular bar is positioned such that the apex of the two equal sides is placed down between the adjacent rollers with the hypotenuse surface facing upwardly to bridge the gap across the hitch. Because the length and width of a hitch will vary depending on the width of the conveyor belt and the conveyor system setup, the above described triangular bar hitch guard generally had to be custom fabricated on site to ensure proper dimensions.
Another problem resides in the tolerance provided between the above-described hitch guard and the adjacent moving belt surface, which can allow small debris to become lodged between the hitch guard and the belt surface causing damage to the belt as the moving belt surface continuously rubs against the trapped debris. To address this problem, breakaway transfer devices are known. With the above-described device, lag bolts were utilized to releasably mount the triangular bar hitch guard to the support plate members or stringers of the conveyor frame structure of the conveyor system. The lag bolts would shear under sufficient force so the hitch guard bar would break away to avoid belt damage.
One drawback of the above-described break-away hitch guard and other transfer devices such as disclosed in U.S. Patent Application Publication No. 2007/0023257 to Schiesser, is the manner in which the devices are mounted to break away during conveyor operations. Transfer devices that have their break-away mountings at the side support plate members or stringers of the conveyor system require that the longitudinally directed forces on the transfer device be redirected and transmitted through the device laterally to the remote break-away mountings. As is apparent, this can be a problem where the impacts or jams with the transfer device occur at a more laterally central location making the device less likely to break-away before the belt is damaged.
Another drawback with these break-away hitch guards is that in the event that the hitch guard breaks away, the hitch guard completely loses functionality requiring replacement of the entire hitch guard. In one transfer device disclosed in U.S. Pat. No. 3,548,996 to Ellis, a complex series of narrow, relief plates are individually removably attached by magnets to corresponding individual slidable mounting blocks having shafts that allow longitudinal movement in the direction of belt travel. This is a very complicated and expensive system, and by allowing longitudinal movement, this system is configured so that debris would enter the gap in the belt conveying surface.